2. STOCK-BASED COMPENSATION (Details Narrative) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				9 Months Ended
	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2017	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Stock-based compensation costs capitalized as part of inventory	$ 0			$ 0	$ 0	$ 0
Intrinsic value of options exercised	214			154	$ 959	564
Weighted average remaining contractual life of the options exercisable and expected to be exercisable					3 years 5 months 1 day
Stock Option and RSU Transactions
Stock-based compensation expense related to stock options and RSUs	$ 206			$ 232	$ 614	$ 695
Restricted Stock Units granted (in thousands)	0	0	64	0	64	157
Market value on the date of the grant					$ 3.93	$ 1.78
Restricted Stock Units vested (in thousands)	4				11
Restricted Stock Units unvested (in thousands)	85				85
Restricted Stock Units unvested intrinsic value	$ 194				$ 194
2016 Equity Incentive Plan
Unrecognized stock-based compensation	1,120				1,120
Estimated forfeitures of unvested stock based awards, amount	3				$ 3
Weighted average period for recognition of costs					2 years 4 months 24 days
Employee Stock Purchase Plan
Weighted average period for recognition of costs					1 month 6 days
Stock-based compensation related to the ESPP	36			$ 25	$ 208	$ 96
Compensation cost related to purchase rights under the ESPP but not yet recognized	$ 13				$ 13
ESPP purchase right granted (in thousands)	0			0	0	0
ESPP shares issued (in thousands)					116	65
ESPP shares available for issuance (in thousands)	265				265